Synergistic antioxidant compositions



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Charles C. Shepherd, Ethyl Corporation, of Delaware Birmingham, Mich, assignor to New York, N. Y., a corporation No Drawing. Application December 2, 1955 Serial No. 550,786

2 Claims. (Cl. 44-69) This invention relates to antioxidant compositions and to oxygen-sensitive media containing the same.

It has been found heretofore that 4-(isopropylamino)- diphenylamine is an elegant stabilizer for alkyllead antiknock agents. This compound very effectively inhibits oxidative deterioration of lead alkyls even under severe conditions.

It has also been discovered that 2,6-di-tert-butylphenol has outstanding potency as an oxidation inhibitor for tetraalkyllead antiknock compounds, tetraalkyllead antiknock fluids and stable gasolines such as aviation gasoline and the more modern motor gasolines containing these tetraalkylead compositions.

It has now been discovered that mixtures of 4-(isopropylamino)-diphenylamine and 2,6-di-tert-butylphenol possess a number of unexpected and important advantages rendering them eminently suited for antioxidant utilities.

An object of this invention is to provide synergistic antioxidant compositions. Another object is to provide particularly effective means for preventing oxidative deterioration of alkyllead antiknock compounds and fluids. A further object is to provide concentrated alkyllead antiknock compositions which are especially stable on storage, even when in contact with oxygen, air or ozone. An additional object is to provide gasoline which is stable against oxidative deterioration. Still another object is to provide leaded gasolines which are stable when in con tact with oxygen, air or ozone. Other objects will be apparent from the ensuing description.

The above and other objects are accomplished by providinga synergistic antioxidant composition consisting essentially of 4-(isopropylamino)-diphenylamine and 2,6- di-tert-butylphenol.

This invention has resulted in important advantages in the art of antioxidation. In the first place the compositions of this invention are synergistic in antioxidant function-i. e. in the use of mixtures of 4-(isopropylamino)- diphenylamine and 2,6-di-tert-butylphenol results in a greater than additive efiect. This is a very important discovery because it represents a mutual enhancement of antioxidant effectiveness of materials, each of Which in its own right is particularly effective as an inhibitor of oxidative deterioration. This discovery is particularly unexpected because it has heretofore been found that antioxidants of various types are not ordinarily cumulative in eifect and the effect of a combination of antioxidants of various types cannot be predicted from considerations of the effects of the individual agents when these agents are used alone.

Another advantage of this invention is its widespread applicability. For example, the synergistic compositions of this invention are capable of stabilizing alkyllead antiknock compounds, antiknock fluids containing alkyllead antiknock compounds, unstable gasolines (whether clear or leaded) and stable gasolines containing an alkyllead antiknock compound, the presence of which renders the leaded gasoline susceptible of oxidative deterioration. In

2,865,722 Patented Dec. 23, less these media the synergistic antioxidant effects inherent in the compositions of this invention persist.

One embodiment of this invention is an antiknock composition comprising an alkyllead antiknock compound normally tending to deteriorate in the presence of oxygen and, as a stabilizer therefor, a small stabilizing amount of 4-(isopropylamino)-diphenylamine and 2,6-di-tertbutylphenol. Such antiknock compositions preferably contain a scavenger complement, although this is not essential to this embodiment since it is often desiredIto store an alkyllead compound in substantially pure state for long periods of time. This aspect of the invention makes this possible by virtually eliminating oxidative deterioration of lead alkyls.

Another embodiment of this invention is gasoline normally tending to deteriorate in the presence of oxygen containing, in amount suflicient to inhibit such deterioration, a small antioxidant quantity of 4-(isopropylamino) diphenylamine and 2,6-di-tert-butylphenol.

Another embodiment of this invention is leaded gasoline normally tending to deteriorate in the presence of oxygen containing, in amount sufiicient to inhibit such deterioration, a small antioxidant quantity of 4-(isopropylamino)-diphenylamine and 2,6 di-tert-butylphenol. In this embodiment the gasoline can itself be inherently unstable in the presence of oxygen or can be a stable gasoline which does not tend to deteriorate in the presence of oxygen containing an antiknock quantity of an alkyllead antiknock compound, the presence of which renders the leaded gasoline susceptible of oxidative deterioration. In this latter medium the synergistic antioxidant compositions of this invention focus their inhibitory action both upon the resulting instability of the normally stable gasoline and upon the alkyllead antiknock compound itself.

In the above compositions of this invention it is preferred to employ 4-(isopropylamino)-diphenylamine and 2,6-di-tert-butylphenol in a weight ratio from between about 9 to l to about 1 to 9 respectively because with these ratios the mutual enhancement of antioxidant activity is very pronounced. However, other ratios can be effectively employed.

To prepare the synergistic antioxidant compositions of this invention suitable quantities of 4-(isopropylamino) diphenlylamine and 2,6-di-tert-butylphenol are placed in an appropriate container and mixed. The resulting mixture may be used as such by appropriate blending techniques, although a formulating solvent is usually advantageous.

In the preparation of the improved alkyllead antiknock compositions of this invention the several principal ingredients-tetraalkyllead antiknock compound, scavenger complement (if used), 4-(isopropylamino) -diphenylamine and 2,6-di-tert-butylphenol are introduced into a suitable container and mixed. The order of addition of ingredients during formulation is not critical.

In preparing the improved gasolines of this invention the synergistic stabilizers of this invention are blended in appropriate quantity with the gasoline, the 4-(isopropylamino)-diphenylamine and 2,6-di-tert-butylphenol being used either as a preformed blend or being added separately in either order. If the gasoline is to be leaded the tetraalkyllead antiknock compound or antiknock fluid containing the'same can be subsequently blended with this treated gasoline, the antiknock compound or fluid can be added to the gasoline beforethe synergistic antioxidant composition, the various ingredients of the finished fuel can be blended with the gasoline in various sub-combinations in any sequence or an improved antiknock composition of this invention containing the mixed antioxidants can be blended with the gasoline.

l ypic al synergistic antioxidant compositions of this invention are presented in Table I.

Table I.- Synergistic antioxidant compositions 2,6-Di-tertbutylphenol,

4-(Isopropylamino)-dipheny1amine, Parts by Weight Parts by Weight Representative alkyllead antiknock compositions of this invention are presented in Table II. The figures following the representative ingredients are parts by weight. The two figures following the synergistic stabilizing ingredients show respectively the amounts which are used'to obtain a composition containing 0.01 and 2.0 percent by weight of combined stabilizer based on Qthe lead alkyl antiknock agent. The relative proportions of each of the'ingredients of this combined stabilizer can be varied as shown in Table I. If the lower figure following the combined stabilizer shown in Table II is increased by a factor of 10, the resulting alkyllead antiknocl; composition will contain 0.1 percent by weight of the combined stabilizer based on the lead alkyl whereas one-half of the second figure provides a composition containing 1.0 percent. Should other concentrations be desired the proper adjustments are evident.

Table lI.--Antiknck fluid compositions Antiknook Agent Scavenger Stabilizer Tetramethyllead 267-- None 4-(Isopropylamino)-diphenylamlne 2,6-

di tert butylphenol 0027-534. Do Etzlglene dibromide Do. Do Ethylene dibromide Do.

94 and ethylene dichloride 99. Tetraethyliead 323.... None 4-(Isopropylamino)-diphenylamine 2,6- di tert butylphenol 0.032-6A6. Do Etllglene dibromide Do. Do Ethylene dibromide Do.

9e and ethylene dichloride 99. Do. Ethylene dihromide D0.

113 and ethylene dichloride 99. Do Mixed dibromotolul- Do.

enes 200. Do Mixed dibromotolul- Do.

enes 125 and ethylone dichloride 99, Do Mixed dibromotolu- Do.

enes 150 and 1,2,4- trichlorobenzene 175. D0 Ethylene dibromide Do.

' 94 and mixed triohlorobenzenes 140. Do 1,421;s Dibromobutane D0. D0 1,4 Dibromobutane Do.

7 108 and lA-dichlorobutane 127. Tetrapropylleed 379--- Acetylene tetrabro- 4 (Isopropylamino) mide 346. V diphenylamine+ 2,6-di-tert-butylphenol 00384.58. Dimethyldiethyl- B,fl-Dibromodiothyl -tlsopropylaminay lead 295 ether 232. diphenylamine+ 2,6di-tert-butylphenol 0.030-5.90. Methyltnethyllead 6,fi'-Dibromodiiso- 4-(Isopropylamino)- 309. propyl ether 130 diphenylamine and B,B-dichloro- 2,6-di-tert-butyldiethyl. ether 143. phenol.

- has occurred during The antiknock fluid compositions shown in Table II are presented for illustrative purposes only. Other antiknock fluid compositions will now be apparent to one skilled in the art. In all instances the presence of the mixtures of 4-(isopropylamino)-diphenylamine and 2,6- di-tert-butylphenol enhances the stability characteristics of the formulations over those characteristics prevailing in the absence of any stabilizer or when using the same amount of either of the stabilizers separately.

Improved unleaded fuel compositions of this invention are prepared by blending amounts of the synergistic inhibitor compositions of this invention between about 0.001 to about 1 percent by weight in various unleaded gasolines normally susceptible of oxidative deterioration. A wide variety of gasolines can be improved in this manner, for example, gasolines having the following characteristics:

A 100% catalytically cracked gasoline having an initial boiling point of 105 F. and an end point of 425 F.

To prepare the improved leaded gasolines of this invention the improved composite additives shown in Table II are blended in appropriate quantity with unleaded gasolines such as those described above or inherently stable gasolines. If desired, the various ingredients of these composite additives can be blended with such gasolines separately or in sub-combinations.

The ingredients of the synergistic antioxidant compositions or" this invention are effective as inhibitors when used alone. The potency of 4-(isopropylamino)-diphenylamine as an alkyllead stabilizer is illustrated by the results of accelerated fluid storage tests. Portions of an antiknock fluid consisting essentially of tetraethyllead, 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride were placed in glass bottles containing percent outage; that is, the bottles contained 80 percent by volume of air. The term theory represents the quantity of these halogens theoretically required to react with the lead to form the corresponding lead halidei. e. two atoms of halogen per atom of lead. Small measured amounts of 4-(isopropylamino)-diphenylamine were added to individual samples of the above antiknock fluid and these samples, together with control samples--i. e., stabilizer-free antiknock fluids-were stored at 50 C. for a period of 168 hours. The amount of fluid decomposition was found by determining the ammonia soluble lead contents of the samples by chemical analysis. Basically, the method involves extracting from the samples all lead salts formed during storage by means of an ammonia-ammonium acetate solution and assaying the amount of such salts in the extract by conventional means. Thus, the method provides a reliable measure of the amount of decomposition which the storage test described above. The results are shown in Table III.

Table 1Il.Stabilizati0n of anti/mock fluid with 4-(isopropylamino)-diphenylamine Fluid Deeom- Reduction in Cone. of Stabilizer, wt. percent of position, g. Fluid Decom- TEL Pb per ml. position, TEL percent The results shown in Table 111 show, the outstanding effectiveness of 4- (isopropylamino) -diphenylarniner as an inhibitor for lead alkyl antiknock agents. considerably inferior results are obtained when the above tests are repeated using the same concentrations of 4-aminodiphenylamine or of diphenylamine.

2,6-di-tert-butylphenol is a particularly effective tetraalkyllead stabilizer. This compound is much more effective than trialkylphenols which have been proposed and used as antioxidants. By way of example, individual gasoline samples containing 3 milliliters of tetraethyllead per gallon as an antiknock fluid consisting essentially of tetraethyllead, ethylene dibromide and ethylene dichloride and 7 containing either 2,6-di-tert-butylphenol or 2,6-ditert-b'utyl-4-rnethylphenol in amount equivalent to 2 pounds per 100 barrels were subjected to storage at 110 F. for 18 weeks. The gasoline used in these tests was a modern motor gasoline which was resistant to oxidation when unleaded. The scavenger complement of these leaded fuels was present in amount such that there were 0.5 theory of bromine and 1.0 theory of chlorine. The amount of antiknock fluid decomposition which occurred during these storage tests was found by determining the alkyllead salt contents of the samples by chemical analysis. These salts were extracted from the gasoline with nitric acid, converted into inorganic lead salts and determined by a spectrophotometric method. The results are shown in Table IV.

Table I V.Eflect of phenolic inhibitors on tetraethylledd decomposition during storage It is obvious from the data in Table IV that 2,6-di-tertbu'tylphenol is well over 300 percent as effective as 2,6- di-tert-butyl-4-methylphenol in retarding oxidative deterioration of tetraethyllead. Since 2,6-di-tert-butyl-4-methylphenol is representative of 2,4,6-trialkyl phenols as a class and possesses an antioxidant potency typical of the class, it is clear that the superior eifectiveness of 2,6-ditert-butylphenol is a distinct technical advantage. Thus, in achieving a synergistic eifect between the highly effective inhibitors used in the antioxidant compositions of this invention there is now provided a still further improvement in the art.

To illustrate the unexpected synergistic potency of "the compositions of this invention recourse was had to the standard method of the American Society for Test Materials for the determination of the oxidation stability of gasoline (Induction Period Method) ASTM Designation: D52546, as fully described in Part III-A, ASTM'Standards for 1946-. According to this method, the induction period is the period during which there is no drop in pressure indicating no absorption of oxygen, when the 'test material is placed in a test bomb maintained at a temperature of 100 C. with an initial pressure of 100 pounds per square inch gage of oxygen.

In these tests six different base gasolines were used ranging from a highly unstable gasoline to an essentially oxygen-insensitive gasoline. All of these fuel samples contained 3.0 milliliters of tetraethyllead per gallon as the antiknock fluid described in connectionwith the preceding series of tests. In Table V, Fuel A was a blend of 90 percent of catalytically cracked and 10 percent of polymer gasoline blending stocks having an induction period (leaded as above) of-115 minutes. FuelB was a gasoline blend of high olefinic 'content'having an end 6 point of 390 F. When leaded as above this fuel had an induction period of 215 minutes. Fuels C, D, E and F were commercial motor gasolines having induction periods when leaded of 305, 500, 890 and 925 minutes respectively. Varying concentrations of synergistic antioxidant compositions of this invention were blended with the above gasolines and the induction periods measured. The calculated induction periods were obtained by adding the observed individual induction periods of the two in- 1n hibitors when used separately at the concentrations corresponding to their individual concentrations in the mixtures and substracting the induction period of'the leaded gasoline without any inhibitor. The difference between the found or observed induction period and the calculated induction period is known as the induction period increase (I?!) and is a direct measure of the synergistic effect produced by the cooperation between the two inhibitors when used in concert. The results of these tests are shown in Table V.

l able V.E17ect of antioxidants on induction period of leaded gasolines Antioxi- Induction dant Period, min. IPI, Fuel Antioxidant cone, lb. min.

per 1,000

bbl. Found Cale.

IA-DA stands for 1-(isopropylarnino)-diphenylamine. 2 DTB stands for 2,6-di-tert-butylphenol.

Referring to the data'shown in Table V it is clear that in "all instances a synergistic eifect was obtained. The degrees -of this mutual enhancement of antioxidant activity were very pronounced. It is pointed out in U. S. Patent 2,160,851 that an induction period of '50 minutes is equivalent to a stabilization under atmospheric conditions and even constant exposure to sunlight for a period in excess of 6 months. Therefore, the induction period increases shown in Table V represent a substantial increase in the useful life of the various leaded fuels.

Generally speaking, the mixed inhibitors of this invention exhibit a larger synergistic eifecti. e. the IPI 'is gre'aterwhen they are used at a concentration in leaded gasoline equivalent to from 10 to about 35 pounds of total inhibitor per thousand barrels of gasoline than when the concentration is equivalent to from about 2 up to 10 pounds per thousand barrels. Consequently, this former concentration range is preferred for use in most leaded gasolines, especially those gasolines which have induction periods from about 100 to about 1200 minutes when containing from about 1 to about 3 milliliters of tetraethyllead per gallon in the absence of an inhibitor.

The results shown in Table V are illustrative of the enhanced stability characteristics of the composition of this invention. Equally good results are obtained with other compositions of this invention such as those described in Table II and unleaded oxygen-sensitive gasolines containing my synergistic antioxidant compositions.

Other advantages of the mixed inhibitors of this invention include freedom from induction system deposit problems; 'obviation of low temperature varnish and sludgeformation on engine parts, such as piston skirts; and water and caustic insolubility, which means that gasoline towhich these mixed inhibitors have'been added are-not'deprived of the antioxidant materials upon contact butane; 1,4 dichloropentane; ether; [LE-dichlorodiethyl ether; trichlorobenzene; bromotoluenes; tert-butyl bromide;

dichloro 1 2 hydroxyethane;

: Patents I about 0.5 to about the quantity required to react with the lead to form lead ,halide-i. e. 2 atoms of halogen per atom of lead. This amount can be in the form of a single compound or a mixture of compounds. However, when I use mixtures of Patent 2,398,281.

with water or dilute alkali solutions encountered under refining and storage conditions. The alkylead antiknock agents which are stabilized according to certain embodiments of this invention are represented by such compounds as tetramethyllead, tetracthyllead, tetrapropyllea d, tetrabutyllead, dimethyldiethyllead, trimethylethyllead, and the like, or mixtures thereof. Such compounds containing from 4 to about .16 carbon atoms, one atom of lead and a plurality of lead to carbon bonds, are capable of increasing the octane quality of gasoline when employed therein in antiknock quantities-0.02 to 6.5 grams of lead per gallon. Of such compounds, tetraalkyllead compounds having from 4 to about 12 carbon atoms have superior volatility characteristics from the standpoint of engine induction and are thus preferred. Halogen-containing alkyllead compounds, such as triethylleacl bromide, may also be stabilized according to this invention.

The scavengers which are sarily present in the antiknock fluids and leaded fuels of this invention are organic halide compounds which react with the lead during combustion in the engine to form volatile lead halide. The halogen of these scavengers has an atomic weight between 35 and 80; that is, the active scavenging ingredient is chlorine and/or bromine. Such scavengers include ethylene dibromide, ethylene dichloride; carbon tetrachloride; propylene dibromide; 2 chloro 2,3 dibromobutane; 1,2,3 tribromopropane; hexachloropropylene; mixed bromoxylenes; 1,4-dibromo- 3,5 dibromodiisopropyl di- 2-methyl-2-bromobutane; 2,3,3-trimethyl-2-bromobutane; tert-butyl chloride; 2,3-dimethyl-2,3-dibromobutane; 2,3-dimethyl-2,5- dibromohexane; 2-methyl-2,3-dibromobutane; 2-methyl- 2,3 dichloroheptane; 2 methyl 2,4 dibromohexane; 2,4 dibromopentane; 2,5 dichlorohexane; 3-methyl- 2,4 dibromopentane; 1 phenyl 1 bromoethane; 1- phenyl 1 chloroethane; ethyl ocbromoacetate; diethyl dibromomalonate; propyl a chlorobutyrate; 1,1- nitroethane; 1,1 dichloro 2 nitroethane; 1,1 dibromo 1 nitrobutane; 2 chloro 4- nitropentane; 2,4 dibromo 3 nitropentane; 1 chloro- 1 bromo 3 hydroxypropane; 1- bromo 3 hydroxybutane; 3 methyl 2 bromo 4- hydroxypentane; 3,4 dimethyl 2 bromo 4 hydroxypentane and, in general, scavengers disclosed in U. S. 1,592,954; 1,668,022; 2,364,921; 2,479,900; 2,479,901; 2,479,902; 2,479,903; and 2,496,983. In short, it is preferred to employ halogenated scavengers containing only carbon and elements selected from the group 1 consisting of hydrogen, joxygen. hydrocarbons, that is, bromohydrocarbons,

bromine, chlorine, nitrogen and Particularly preferred scavengers are halochlorohydrocarbons and bromochlorohydrocarbons having a vapor pressure of 0.1 to 250 millimeters of mercury at 50 C. The total amount of scavenger used is preferably from 2.0 theories, a theory being defined as bromine-containing and chlorine-containing scavengers,

particularly bromoand chlorohydrocarbons as the scavenger complement, I can employ a wider range of concentrations in the proportions described in U. S. Thus, the scavenger concentrations used are those which are sufficient to control the amount Although 4-(isopropylamino)-diphenylamine and 2,6-

preferably, but not neces- I of deposits formed in the engine, particularly on the exhaust valves.

both inhibitors. of inhibitors in the leaded andunleaded gasoline embodiments of this invention are between about 0.001 to about 2 percent'by weight. These amounts may be varied-depending upon the degree of instability of the gasoline and the type of conditions or service to be encountered. In the concentrated alkyllead embodiments of this invention amounts between about 0.01 and about 2.0 percent by weight based on the weight of the alkyllead compound are satisfactory. Again, variations in these amounts are permissible and sometimes advantageous. For example, when the alkyllead antiknock compound or fluid is to be stored for unusually long periods of time under severe oxidizing conditions, higher concentrations of the mixed inhibitors of this invention are useful. Thus, in general the amount of the mixed inhibitors used in the alkyllead antiknock compounds and fluids and clear or leaded gasolines herein described is that which is sufficient to inhibit deterioration of these media when they are placed in contact with air.

The fluid and fuel embodiments of this invention may contain other ingredients, such as dyes for identification purposes; metal deactivators, such as N,N'-di-salicylidene- 1,2-diaminopropane, etc.; other antiknock agents, such as the carbonyls of iron, nickel, and like elements, aromatic amines, such as N-methyl aniline, xylidine, etc.; anti-icing and anti-rust additives; surface ignition control additives, such as esters of phosphorus acids; and the like.

The mixed inhibitors of this invention may be blended in the dry state with gasoline or antiknock fluids. However, it is advantageous to employ the mixed inhibitors in the liquid state. This is done by dissolving these mixed inhibitors in a suitable solvent. Particularly suitable solvents include acetone, methylethyl ketone, methanol, ethanol, isopropanol, methyl isobutyl carbinol, benzene, toluene, xylene and the like. In general, ketones and alcohols containing up to about 6 carbon atoms and aromatic hydrocarbons containing from 6 to about 18 carbon atoms are excellent solvents. Not only are such formulations very useful in blending operations because high concentrations of the mixed inhibitors of this invention are soluble therein, but these formulations can be stored for long periods of time without deterioration so long as reasonable storage precautions are taken.

The leaded fuel embodiments of this invention normally contain from about 0.02 to 6.5 grams of lead per gallon although gasolines containing higher concentrations of lead alkyls are also stabilized by employing therein the synergistic inhibitors of this invention.

Because of the outstanding results achieved from the combination of 4-(isopropylamino)-dipheuylamine and 2,6-ditert-butylphenol this invention has been described in relation to these materials. Good results are obtained by totally or partially replacing 4-(isopropylamino)-diphenylamine in the compositions of this invention with 4-(sec-butylamino)-diphenylamine.

The preparation of 2,6-di-tert-butylphenol is described in U. S. Patent 2,459,597.

4-(isopropylamino)-diphenylamine may be prepared by the reductive alkylation of 4-nitrodiphenylamine with acetone and hydrogen in the presence of a suitable catalyst, such as copper chromite. In practice the reaction is conducted at elevated temperature and pressure using from about 5 to 10 moles of acetone in excess of each mole of 4-nitrodiphenylamine present. Normally, temperatures in the range of about to about 200 C. and pressures in the order of about 500 to about 2000 p. s. i. gauge are used. Among the several methods for the preparation of 4-nitrodiphenylamine is that of condensing aniline with p-chloronitrobenzene.

I claim:

1. Gasoline containing an antiknock quantity of an alkyllead antiknock-compound :nprmallyl tending. to de- In general, suitable amounts of thispain teriorate in the presence of oxygen containing, in amount suflicient to inhibit such deterioration, a small antioxidant quantity of a synergistic antioxidant composition consisting essentially of 4-(isopropylamino)-diphenyl amine and 2-6-di-tert-butyl phenol, the weight ratio of 4-(isopropylan1ino)-diphenyl amine to 2,6-di-tert-butyl phenol being from between about 9:1 to about 1:9 respectively.

2. A leaded gasoline containing from about 1 to about 3 milliliters of tetraethyllead per gallon, said leaded gasoline having an induction period from about 100 to about 1200 minutes, and in amount equivalent to from 10 to about 35 pounds per 1000 barrels of said leaded gasoline, a synergistic antioxidant composition consisting essentially 10 of 4-(isopropylamino)-diphenyl amine and 2,6-di-tertbutyl phenol, the weight ratio of 4-(isopropylamino)- diphenyl amine to 2,6-di-tert-butyl phenol being from between about 9:1 to about 1:9 respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,395,382 Walters Feb. 19, 1946 2,410,847 Walters Nov. 12, 1946 2,459,597 Stillson et al. Jan. 18, 1949 2,552,466 Sweeney May 8, 1951 2,618,612 Howell et a1 Nov. 18, 1952 2,734,808 Biswell Feb. 14, 1956 

1. GASOLINE CONTAINING AN ANTIKNOCK QUANTITY OF AN ALKYLLEAD ANTIKNOCK COMPOUND NORMALLY TENDING TO DETERIORATE IN THE PRESENCE OF OXYGEN CONTAINING, IN AMOUNT SUFFICIENT TO INHIBIT SUCH DETERIORATION, A SMALL ANTIOXIDANT QUANTITY OF A SYNERGISTIC ANTIOXIDANT COMPOSITION CONSISTING ESSENTIALLY OF 4-(ISOPROPYLAMINO)-DIPHEYL AMINE AND 2-6-DI-TERT-BUTYL PHENOL, THE WEIGHT RATIO OF 4-(ISOPROPYLAMINO)-DIPHEYL AMINE TO 2,6-DI-TERT-BUTYL PHENOL BEING FROM BETWEEN ABOUT 9:1 TO ABOUT 1:9 RESPECTIVELY 